1. Field of the Invention
The invention in question concerns a device for testing components of transparent material for surface irregularities and occlusions by dot-scanning the component by a light ray and detecting the light which is diffracted by the surface irregularities or occlusions.
Components of transparent material, for example optical or ophthalmic lenses, must be tested for flaws prior to their utilization, particularly for surface flaws such as scratches, smears, cracks, chipping, stains, and for occlusions such as bubbles or streaks. Such flaws would limit the usability of a lens if these were to exceed the limit values stated in DIN 3140.
2. Discussion of the Prior Art
Conventionally, the testing of optical components is carried out by personnel in the form of visual inspection. Such a test must be performed, to a large extent, in a darkened room. It is expensive, not sufficiently objective and, due to the high degree of monotony of the testing procedure, not sufficiently reliable.
Efforts have, therefore, been made to develop methods and devices for automatic, objective testing of optical components.
From DE-OS No. 32 37 511, the method of placing optical components to be tested in the optical beam path of a television camera and of displaying through the component, a test pattern on the camera is known. The disturbances caused by flaws in the component, produce a video signal which deviates from the control signal not influenced by the component. The flaw is deduced on the basis of the deviation between the control and actual signal. A device acting on this principle is rather expensive and is not able to detect smaller flaws, for example, those resulting from scratches, smears or hairline cracks.
In order to increase the sensitivity of the testing procedure, it is recommended in DE-OS No. 30 11 014 that the component to be tested be illuminated completely, a television image be produced, and the video signal be analyzed line for line. This method is also not sufficiently exact.
An even older recommendation for a test method is to be found in DE-OS No. 23 37 597. According to this disclosure, a light ray is focused on the surface of the component to be tested and is punctiformly moved over the surface, at the same time being kept in focus. The light penetrating the component is reflected backwards, passes through the component again, and then falls onto a detector. Deviations in the intensity of the receiver signal make it possible to deduce a flaw and also to localize this flaw.
A device acting on this principle is very expensive. It only allows that surface of the work-piece to be tested onto which the scanner ray is focused.